A major effort has been directed towards the development of new synthetic wound dressings which attempt to meet the requirements in the treatment of skin wounds. Such effort is described, for example, in Park, G. B., "Burn Wound Covering-A Review", Biomat. Med. Devices Artif. Organ. 6; 1-35 (1978). An important class of synthetic dressings for wound repair, which is receiving increasing clinical acceptance, are occlusive dressings.
Occlusive dressings are shown to expedite reepithelialization (i.e., growth of new skin tissue) in comparison to gauze, this effect being attributed to the physical properties of the occlusive dressings, according to the Alvarez, O. M. et al, "The effect of occlusive dressing on collagen synthesis and reepithelialization in superficial wound" J. Surg Res., 35: 142-148 (1983). Optimum characteristics desirable in occlusive wound dressings are: (1) adherence to non-wounded skin, (2) permeability to oxygen and water, and (3) ability to exclude bacteria, combined with a high absorptivity of fluids, according to Silverman, R. A. et al, "Effects of occlusive and semiocclusive dressings on return of barrier function to transepidermal water loss in standardized human wounds", J. of American Academy of Dermatology, 20, 755-760 (1989). Other authors, e.g., Quinn, K. J. et al "Principles of burn dressing", Biomaterials, 6: 369-376 (1985) and Park, G. B. cited supra states that the development of an adhesive that does not function as a moisture transmission barrier but is sufficiently permeable to allow absorptivity of wound exudate would be highly desirable and would also potentially have the following properties: (1) extended adhesion to wound surface (2) high absorption of wound fluids with concomitant loss of adhesive properties when in contact with a wet wound, and (3) provision of a non-cytotoxic substratum to support normal adhesion of mammalian fibroblasts and keratinocytes, and (4) complete removability of the dressing without causing any damage to the wound.
Occlusive wound dressings generally fall into one of two classes. Dressings in the first class are composed of an absorbent or non-absorbent material and an adhesive in separate layers (the adhesive constituting the outside layer) on a polymeric (e.g., polyurethane) backing. Such wound dressings are disclosed, for example, in Wheeland, R. G., "The newer surgical dressings and wound healing", Dermatologic Clinics, 5(2), 393-407 (1987). The second class are dressings comprising an adhesive blend, which in turn comprises an adhesive material (typically a pressure sensitive material) and a moisture absorbing material, on a polymeric film backing layer. Representative references are U.K. Patent No. 1088992 and published U.K. Patent application GB 2198441A. U.K Patent No. 088992 describes an adhesive blend which comprises a water soluble or water swellable hydrocolloid and a water insoluble viscous elastic binder, on a backing of a water-impervious material. Published U.K Patent application GB 2198441A describes a dressing of this type in which the adhesive blend comprises a pressure sensitive adhesive material (e.g., an acrylic adhesive) and an alginate, which may be either water soluble (preferred) or water insoluble. The alginate renders the pressure sensitive adhesive blend highly water absorbable. The adhesive blend or layer may also contain a medicament. The backing layer comprises a water impervious but moisture vapor transmitting continuous polymer film, e.g., polyurethane.
U.S. Pat. No. 4,593,053 to Jevne et al describes hydrophilic, skin-compatible, pressure sensitive, solid, adhesive hydrogel compositions, comprising 25-50 weight per cent (preferably about 30-40 weight percent) polyvinyl pyrrolidone (PVP), about 2-5 weight percent (preferably about 3-4 weight percent) polyvinyl alcohol (PVA), about 5-40 weight percent polar plasticizer or humectant, about 3-50 weight percent water, and optionally (depending on the application) a pharmaceutically effective amount of a desired drug or sufficient ionic species to provide conductivity to the composition. These compositions are disclosed as being useful in biomedical applications including wound dressings.
D. J. Smith et al, in J. Polymer Sci. Polymer Letters Edition, 23, 633-637 (1985) and in U.S. Pat. No. 4,781,921, disclose hydrophilic hydrogels which are cross linked polymers of entprol methacrylate (also known as "Quadrol" methacrylate) and entprol dimethacrylate (also known as Quadrol dimethacrylate). ["Quadrol" is a trademark [BASF] for the compound N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine]. Also disclosed are the corresponding monomers and the precursors N,N'-bis(2-hydroxypropyl)ethylenediamine and N,N'-tris(2-hydroxy propyl)ethylenediamine. The former is made by reaction of 2 mols of propylene oxide with one mol of ethylenediamine and the latter is made by reacting the former precursor with one additional mole of propylene oxide. The hydrogel polymers have macrophage activity and are useful in wound dressings, as disclosed in U.S. Pat. No. 4,781,921, but are non-adhesive.
H. K. Pokharna et al, Journal of Bioactive and Compatible Polymers, 5, 42-52 (1990) describes copolymers of hydroxyethyl methacrylate (HEMA) with "Quadrol" methacrylate and with Various aminoalkyl methacrylamides as substrates for growth of fibroblast cells. The materials tested differed in their capacity to support fibroblast cell growth.
A major limitation of occlusive dressings is that the adhesive layer or adhesive component of a blend, as the case may be, tends to reduce the absorption of fluids in wounds and the moisture transmission rate. Occlusive dressings tend to accumulate wound exudate and may adhere to the wound site.
While desirable characteristics of a material for a wound dressing and other biomedical applications which is both adhesive, hydrophilic and capable of absorbing fluids have been identified in the literature, such characteristics have not been fully achieved in practice. There exists a need for a material which combines all of these characteristics.